The Sleep & Brain Health Connection


Article At-A-Glance:

  • Although your mind is unconscious, your body and brain remain busy during sleep. Sleep is broken down into 4 key phases, and each phase has a specific function.
  • Stage 1 and 2 are phases of light sleep. During this time your body temperature drops, and you disengage from your surroundings.
  • In Stage 3 there is a major change in your brain during sleep. You enter deep sleep, and your body begins a restorative process.
  • Stage 4 or REM sleep is the most active phase of your brain while sleeping. During this time you dream and begin to process information.
  • The latest research connecting memory & sleep
  • Practical ways to improve your sleep quality

What Happens When You Sleep

If you've ever wondered what goes on inside your brain during those mysterious hours of sleep, the answer is a lot. Scientists now understand that the body uses this time to undergo several processes that are vital to your health. Physically, your body uses this time to repair itself. Emotionally, sleep is when your body processes memories and solves problems. This may partly explain why we 'sleep on it' before making a big decision.

In order to fully understand what happens when you sleep, however, you have to look at each individual phase. As you fall asleep, your body and brain moves in cycles. There are 4 key phases that you rotate through as you sleep, and each one of them performs a specific function.

Sleep and The Brain: 4 Key Phases

A complete sleep cycle takes an average of 90 to 110 minutes, and during that time we go through 4 distinct stages of sleep. There are three stages of non-REM sleep and one stage of REM (rapid eye movement). Amazingly, we go through this entire cycle somewhere between 4-6 times a night!

Not all sleep cycles are the same. The first 2-3 sleep cycles per night have a relatively short REM sleep period. As the night wears on, your REM cycles will last longer and longer, and your deep sleep actually decreases.


Non-Rem Sleep — About 75% of our sleep time is spent in non-REM sleep, which include 3 key phases:

Stage 1: In this short phase, which typically lasts between 5-15 minutes, you become drowsy and your muscle activity slows. At this point you're slipping into sleep, but your sleep is rather shallow. It's also easy for you to be woken up at this point.

Stage 2: This is also a phase of light sleep, but at this point you're beginning to get ready for deep sleep. Your body temperature drops, and you begin to lose awareness of your surroundings.

The first and second stages of sleep are periods when your body gradually relaxes, disengages from the world, and acclimates itself to the sleeping state. Because these periods take only about 20 to 30 minutes to complete, this is generally thought to be the optimal length of time for cat naps or power naps, as the body will awaken from these stages in a refreshed, alert state, without any grogginess.

Stage 3: This is deep, Delta wave sleep. Delta waves are the lowest brain waves. It is difficult to rouse someone when they are in this stage of sleep. If someone did wake you up at this point, you might feel confused or disoriented. During deep sleep your blood pressure drops, your breathing slows down, and your muscles relax.

Stage 3 is a period of critical importance because this is when the body restores itself. In this time, you repair and regrow tissue, develop muscle and strengthen your immune system. Stage 3 is also when your energy stores are restocked, and you regulate various hormones.

REM Sleep — About 25% of your time is spent in REM sleep.

Stage 4: It may surprise you to learn that REM sleep is the only period in which you dream. In fact, there are many features unique to this stage. During this time, your breathing will become more irregular and your eyes will flit around in different directions. The cerebral cortex area of your brain essentially disables your body’s movement so you don’t act out your dreams. The first period of REM lasts about 10 minutes. It will then recur about every 90 minutes. The final stage, right before waking, could actually last as long as an hour. Before you wake up, your heart rate and breathing will quicken.

REM sleep is the period of sleep where your brain is most active. It is believed that during REM sleep (as well as deep sleep) we form new memories and consolidate information from the previous day. Some scientific evidence suggests that REM sleep may also be important for us to retain information and things we have learned from the previous day. Studies have shown that if you teach an animal a task during the day and then disrupt its sleep that night, the animal will not be able to remember what it learned.

The Latest Research on Memory & Sleep

In a new study published study, researchers have come one step closer to illuminating the sleeping brain. Researchers from the University of Geneva in Switzerland used functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) to find out how the brain consolidates memories while we sleep.  Key Findings:

  • Memory consolidation occurs in deep sleep
  • In deep sleep, the hippocampus replays the day's memories, sending them to the cerebral cortex, reinforcing those neural pathways.
  • The brain took much more interest in the game wins than the losses. As lead author Virginie Sterpenich explains, while the volunteers slept, they "started to 'think' about both games again, and then almost exclusively about the game they won when they went into deep sleep." Unsurprisingly, the "rewarding" memories (the wins) that the brain stored were easier to recall.

If You Are Having Trouble Sleeping

If getting a good night’s sleep were simply a matter of crawling in bed earlier, then perhaps it wouldn’t be so difficult for so many people. However, for many Americans it’s not that simple. Two suggestions:


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